OTHER ANSWERS

There are not any specific limits to the size of databases or the number of queries or tables, but keep in mind that a large number of big queries to large databases can greatly increase your server loads. If on shared hosting, this could impact other customers and may require a VPS or even a dedicated server depending on what it is rising the server load to. If you are running a large database with a large number of queries, be sure to optimize those MySQL queries as much as possible.